1. Field of the Invention
The present invention relates to a screen transmission device which transmits a computer screen on a PC (Personal Computer) or the like through a network, a method of generating a screen and a computer readable medium.
2. Related Art
There is a system which is connected to a remote computer (hereinafter, referred to as a “remote device”) via a network, receives a display image from the remote device and displays it, transmits information on key inputs or the like performed using a device at hand or the like to the remote device, and can thereby use the remote device as if it were at hand. For example, VNC (Virtual Network Computing) and a remote desktop or a smart display of Windows correspond to this. Such a system can be used to operate a PC which is in widely-spaced room in an office, operate an office PC from outside the office or operate a PC which is located in widely-spaced room in a house from a device at hand and so on.
The development of networks, and wireless networks in particular in recent years is remarkable and a mode of wirelessly connecting a device at hand in the above described system and thereby accessing a remote device from an arbitrary position is becoming generalized. However, in order to exploit to the full the merit of accessibility from an arbitrary position by means of wireless connection, use of a battery constitutes an effective means instead of obtaining a power supply from a wall outlet.
When using a battery, an operating time of the battery is one of important factors in determining usability. Simply increasing the battery capacity can expand the operating time, but it also increases the weight of the device carried around with it and increases inconvenience in carrying around the device. Expanding the continuous operating time without increasing the battery capacity requires power consumption of the device to be minimized.
Conventionally, various methods are proposed to lower power consumption. The simplest method may be darkening the display itself, but when using the device in a bright surrounding environment, there is a problem that darkening the display considerably degrades viewability. As another method, a smart display of Windows allows power to be automatically turned off when the display is not in use for a certain time so as to save the power of the battery. Furthermore, JP-A 2002-323942(KOKAI) proposes not only to automatically transition to a power saving mode when there is no operation for a certain time but also to automatically transition from the power saving mode to a normal mode when a specific application event occurs to thereby make user-friendliness compatible with power saving.
On the other hand, JP-A 2000-341222(KOKAI) describes a power saving method when a device is in operation. According to JP-A 2000-341222(KOKAI), video or coded data of voice is transmitted from a remote terminal to a terminal at hand and when the remaining amount of a battery of the terminal at hand decreases, the remote terminal is informed of the decrease in the remaining amount. Upon receiving the information, the remote terminal changes the coding mode to a power saving mode.
As described above, as the power saving method for a screen reception device, the method of automatically turning off power when the device is not in operation or transitioning to a power saving mode is proposed as in the case of the smart display of Windows and JP-A 2002-323942(KOKAI). However, such a method can realize power saving when the device is not in operation, but when the device is continuously used for a long time, there is a problem that power saving is not realized at all and it is not possible to expand a continuous operating time.
On the other hand, as a power saving method of a device is in operation, a method of changing a power-saving coding mode of an image according to the remaining amount of the battery of the image display terminal is proposed as in the case of JP-A 2000-341222(KOKAI). The “power-saving coding mode” described here refers to a mode of reducing the resolution of an image or reducing color gradation or sending only part of the center of the image. However, there is a problem that reducing the resolution of a computer screen causes characters to be crushed and become hardly legible and in this way, reducing the amount of information on the image itself not only causes the appearance to become poor but also degrades user-friendliness.